Central galaxies in clusters are a unique class of objects. They are usually the largest and most luminous member galaxies and they lie very close to the peak of the cluster X-ray emission [1]}, [2]}. Moreover, in the velocity space they sit near the rest frame velocity of the cluster [3]}, [4]}, [5]}. These characteristics imply that the BCGs are located at the minimum in the cluster potential well.
[6]} found that there is a dependence of the velocity segregation on the magnitude gap. This result means that BCGs in FGs are located closer to the minimum of the cluster's potential well, when compared to BCGs in non-fossil systems. This difference is not found for satellite galaxies, independent on their mass.
